This invention relates to highly aligned inexpensive optical devices including emitters which are useful for generating a narrow infrared/optical beam and detectors for detecting the beam efficiently and accurately.
In electronic circuits information is processed and transmitted from point to point through electrical wires. However, in many situations it is desirable and some times absolutely necessary that information be transmitted through space by electromagnetic waves. The present invention concerns itself with transmission over relatively short distances measured in inches or at most 100 feet through devices which generate or which are capable of receiving narrow beams of electromagnetic radiation. Furthermore, the present invention deals with extremely inexpensive devices in particular LED devices which may be manufactured at costs which amount to a fraction of a dollar per device. These devices are not, however, limited to signaling applications. They can be used as sensors for part counters on a conveyor belt, as precise edge locators, door chimes or switch actuators for controlling lights or appliances in a home. Other devices such as lasers which are capable of collimating light into narrow beams are not viewed as coming under the contemplated disclosure of the present invention.
In particular, the present invention is related to inexpensive emitters and to phototransistors which are useful for receiving emitted energy and for generating an electrical output proportional to the radiation which impinges upon the device. For information transmission, it may be useful to modulate an emitter by turning it on and off to generate a stream of 1's and 0's. The emitted energy may be received by a phototransistor and reconstructed as the original digital information. In other applications there may be provided an array of emitters and receivers which are spaced and arranged oppositely from each other such that light from each emitter reaches a respective preassigned detector without interference from the other emitters. Such arrays are useful for implementing computer touch screens and other control matrixes.
It is seen, therefore, that the infrared beam from each emitter must be highly directional and capable of being aimed in a desired direction accurately. However, present technology and methods for packaging infrared emitters and photo detectors with lens allow the radiating surface of an emitter or the active area of a detector to be assembled inaccurately and inconsistently only. For example, the orientation of the emitting surface to the optical reference of the lens associated with standard LED emitters can vary by +/-50%. Likewise, in a detector the detecting surface could only be oriented to an accuracy of +/-50% relative to its lense optical reference and consequently most of the energy contained in the emitter beam would not be received at the detector surface and converted to an appropriate electrical output.
Prior art devices, furthermore, are packaged so that much of the infrared radiation generated by the emitter tends to disperse through space. Consequently, only a small fraction of the energy reaches a detector which is positioned only inches away resulting in a very low current transfer ratio (CTR) between emitter and detector. The CTR is a ratio based on the quantity of current generated by the emitter in relation to a quantity of current introduced at the detector.